Your guide to reducing the risk of dementia

You cannot alter your age or the genes you are born with, but there are lifestyle changes you can adopt which may reduce your chance of developing dementia by as much as 20%.

The BBC convened a panel of independent experts, chaired by the Alzheimer's Society, which evaluated more than 70 research papers and articles to come up with a series of tips for reducing your risk.

It may sound young, but the age of 35, they suggest, is high time to start thinking about these recommendations. If more of us acted on these, thousands of cases of dementia could be prevented in the future.

There is very strong evidence for the following:

EXERCISE

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Prof Clive Ballard gives his top tips on how to cheat dementia

What is good for the heart is good for the brain. Exercise can have a beneficial effect at any age to help protect against dementia. To help reduce the risk at least 30 minutes of exercise, five times a week is suggested. It does not have to be the gym - a brisk walk is a perfectly acceptable alternative. Whatever form of exercise gets your heart pumping and leaves you somewhat out of breath is doing the trick. Exercise helps maintain a healthy weight and blood pressure, and so is indirectly thought to reduce the risk of dementia.

There is also growing evidence that regular exercise has other health effects such as promoting cell and tissue repair mechanisms including growth of new cells in the brain.

NOT BEING OBESE

Being seriously overweight is deemed a risk factor for developing dementia. This really matters in mid-life - between the ages of 35 and 65. Obesity increases the likelihood of developing Type 2 diabetes - believed to be a risk factor - but whether this causes the disease, or is simply more likely to develop in those who are also more prone to dementia is unclear. Obesity is also associated with higher cholesterol and blood pressure - again, known to be risk factors. You are deemed clinically obese - very overweight - if you have a BMI of 30 and above.

Again, the key here is having consistently raised blood pressure in mid-life - anything above 140/90mmHg. It is thought that this increases the chance of dementia by causing damage to the brain. This may happen as a result of a stroke - in which blood supply to part or all of the brain is cut off - or due to microvascular disease, a condition which slows the flow of blood through the body thereby damaging cells and nerves in the brain. If you are over 40, or have a history of dementia or cardiovascular disease in your family, then get your blood pressure checked regularly.

REDUCE CHOLESTEROL

It is mid-life levels once more which appear to pose the greatest problem. Like high blood pressure, high levels of cholesterol raise the risk of stroke and microvascular disease. But cholesterol is also thought to be involved in the mechanism which causes amyloid protein plaques - the protein deposits that characterise Alzheimer's disease - to build up. Again if you are over 40 or have a family history, get your cholesterol checked. The Department of Health recommends a total cholesterol level of less than 5.0mmol/l.

NOT SMOKING

This had been an area of confusion, as some studies had suggested nicotine could have a protective effect - with the chemical reducing plaques when administered to animals in water. But the way in which we smoke tobacco, and the other chemicals inhaled in the process, negates this benefit. As well as raising the risk of vascular disease - a risk factor for dementia - smoking can result in low oxygen levels in the brain which in turn can promote the production of the protein found in brain plaques.

It is possible the following may have an impact:

ALCOHOL

There is no need to start drinking if you do not already

In fact the studies are quite clear that drinking a modest amount appears to protect against cognitive decline. Moderate drinking is defined as keeping within the recommended daily limits - up to two small glasses of wine for a woman, and three for a man. The problem is that these studies compare drinkers with non-drinkers - and people who abstain may do so for health reasons, which in turn may affect their chances of developing dementia. The message is if you are drinking within your weekly guidelines there is no need to stop, but there is no need to take up drinking or increase the amount you consume, as heavy drinking may in fact increase your risk.

FOLLOWING A MEDITERRANEAN DIET

Several recent studies have highlighted the potential for this diet to reduce the risk of Alzheimer's Disease. It involves eating lots of fruit and vegetables, whole grain foods, fish and plenty of olive oil, but it is relatively low in dairy products and processed foods. Further long term research is needed to confirm the effects of eating this way.

BEING SOCIALLY ACTIVE

Some evidence suggests that an active social life throughout life can be protective, with both the social ties one enjoys with others and non-physical leisure time deemed important. However, examining these factors and designing studies which can separate their effects is very difficult - consequently the conclusions which can be drawn from results are limited. One particular study has found that being single and living alone is a risk factor for dementia: social isolation is thought to have negative effects on health generally, increasing depression and cardiovascular disease.

Studies have also suggested that engaging in non-physical leisure activities such as gardening, and knitting may have a protective effect, a benefit that is likely to accumulate gradually over decades.

But the jury is out on:

BRAIN TRAINING

It sounds both attractive and plausible that giving your brain a "workout" could guard against dementia, and there is some evidence that very intensive brain training under strict conditions can improve specific functions like reasoning and problem solving. But there is no evidence as yet that doing a crossword a day or a number puzzle - or even learning a new language at 50 - will protect against dementia. That does mean they do not - simply that the proof that they do is presently lacking.

VITAMIN SUPPLEMENTS

There is no consistent evidence either way as to whether B vitamin supplements - folic acid, vitamin B12 or B6 - are effective in reducing the incidence of dementia. Research continues. However vitamin E supplements, which it was once hoped could prevent and even reverse early neurodegenerative changes, have not appeared to be effective in trials.

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